Electric fuses



June 5, 1956 R. KELLENDORFER 2,749,405

ELECTRIC FUSES Filed April 27, 1954 INVENTOR. HG. Richard Kellendorfev ATToRm:

United States Patent ELECTRIC FUSES Richard Kellendorfer, Munich, Germany, assignor of onethird to Siegfried Skambraks and one-third to Erik Strasser, both of Munich, Germany Application April 27, 1954, Serial No. 425,951

8 Claims. (Cl. 200-113) My invention relates to electric fuses and more particularly to such electric fuses wherein an electrically conductive liquid medium such as mercury acting between two electrodes in an electric circuit protects against the effect of excess current. In case of an overload the liquid medium vaporizes and interrupts the said circuit.

The known electric fuses of this type were unreliable in the case of high voltages and strong currents particularly as the arising high calefactions effected a sudden and violent, almost explosive evaporation of said liquid medium.

The main object of my invention is to avoid the said and other known disadvantages of such fuses. For this purpose I use a capillary holding a thin filament of the said liquid medium and I introduce electrodes so far into said capillary that only a short filament portion remains between the opposing ends of the electrodes. I also pro vide means to hold a certain supply of said liquid medium forming said filament to compensate for any losses thereof as a result of evaporation.

The said and other objects of my invention will be I more fully understood from the following specification when read with the accompanying drawing wherein several embodiments are illustrated.

In the drawing:

Figs. 1 and 2 show a horizontal section and a cross section along line 22 of Fig. 1, respectively, of one embodiment of my new electric fuse;

Fig. 3 shows a sectional view of a screw-in fuse embodying my invention,

Fig. 4 shows a cross section thereof along line 4-4 of Fig. 3;

Fig. 5 shows a sectional view along line 55 of Fig. 4;

Fig. 6 shows a detail more particularly referred to in the specification, and

Fig. 7 shows a sectional view of a further embodiment of my new electric fuse.

The fuse illustrated in Figs'l and 2 is particularly appropriate for use in electric installations in motor vehicles or the like. it comprises a transparent tubular casing 11 made of glass or any other suitable transparent and electrically insulating material. Centrally located within said tubular casing is a shorter capillary tube 12 and at both sides thereof tubes 13, 14 having a wider boring. The capillary tube 12 is insulated from the adjacent tubes 13, 14 by heat insulating packing rings 15 to safeguard said tubes 13, 14 from damages as a result of unequal heating which will start in the capillary tube 12.

The casing 11 is closed at each end by a metallic contact cap 16, 17, and each of these caps supports an electrode 18 and 19, respectively, which extend in axial direction through the tubes 13 and 14, respectively, into the capillary tube 12 without contacting each other. The said electrodes 18, 19 are preferably twisted from flat wire and their outer end portions reaching deep into the capillary tube 12 are tapered to a smaller diameter so that they will be higher heated by the current and will quicker vaporize the intermediate liquid medium such as mercury in case of an overload.

The electrically conductive liquid medium is provided in such quantity within the casing 11 that it fills completely the capillary tube 12 and only partially the adjoining tubes 13, 14 which serve to store excessive liquid medium for use as liquid filament in the capillary tube 12. Said liquid medium closes the electric circuit between the spaced ends of electrodes 18, 19.

In case of an overload in this circuit or of an arising short-circuit therein the liquid medium in the capillary vaporizes and condensates in the empty space within the tubes 13, 14 which can hold a larger supply of said liquid medium than necessary to fill the capillary tube 12.

If twisted electrodes 18, 19 are used, as mentioned above, the liquid medium assembled in the hollow helical space between these electrodes and the surrounding tubes 13, 14 will hold separated droplike quantities thereof and these droplike quantities of liquid medium will prevent an unintentional escape of said medium from the capillary tube 12 if the same vibrates or is shaken, as well as an unintentional return of said liquid medium from the tubes 13, 14 into the capillary tube 12 after the fuse has reacted to an overload.

To permit inspection of the fuse in the dark the casing 11 as well as the capillary tube 12 are made from a transparent material such as glass, quartz, or the like and a portion of the outer surface of the casing 11 opposite the capillary tube 12 is provided with a phosphorescent cover 21) or the like.

it will be well understood that the capillary tube 12 has to be so selected that the thickness of the filament of liquid medium held therein will correspond to the load to be controlled by the fuse.

The screw-in fuse illustrated in Figs. 3, 4 and 5 comprises a hollow casing 21 with fitting cover 22 both made of a suitable material such as china and tightly connected for example cemented to each other after complete assembly of the fuse. The cover 22 is provided with an inspection opening or window 23. The neck portion of the casing 21 has a customary screw socket 24 cemented thereto and connected to one electrode 25, and also contains a contact pin 26 which is connected to the other electrode 27.

The capillary to hold the electrically conductive liquid medium closing the circuit between the electrodes 25, 27 is a slit capillary formed by two bodies 28, 29, such as glass rods, of circular section or of other suitable cross section. The bodies 28, 29 have ground thereupon in opposing position planes 30 extending in axial direction and distanced from each other to form the said capillary slit. The spacing of said planes 30 and their width will determine the cross section of the filament of liquid medium held in the intermediate slit which cross section is selected in view of the load to be controlled by the fuse.

The lower body 28 rests upon and is cemented to conforming semi-circular beds in projections 31 arranged within the hollow casing 21 in opposing positions and the upper body 29 is held, by, for example cemented into the cover 22 completely closing the window 23 thereof. After such assembly the cover 22 is cemented into the casing 21. At both ends of the bodies 28, 29 the said ground surfaces 311 recede to form a larger slit capillary than that between the central portions of said bodies in order to hold a certain supply of the liquid medium which is intended to compensate possible losses thereof through vaporization or the like.

The said electrodes 25, 27 reach Well into the narrow central portion of the capillary without contacting each other and their ends and the connecting filament of liquid medium may be observed through the window 23.

This observation will be greatly eased by a cylindrical shape of the bodies 28, 29 which will enlarge the view of the electrodes and of said filament. A phosphorescent layer or the like 34 will permit an inspection even in the dark. In case of an overload or of a short-circuit the liquid medium between the electrodes 25, 27 will evaporate and will condensate as a drop 32 within the casing 21.

The bodies 28, 29 may have any other than a circular cross section for example as shown in Fig. 6 or a com pletely or partially polygonal cross section.

Fig. 7 shows a fuse having a differently shaped casing 21 and different current supply leads. One electrode is connected to the contact pin 26 and the other electrode to a metallic cap 33 which is cemented to the cover 22. Otherwise this embodiment is substantially identical with the embodiment shown in Figs. 3 to and the same reference numerals indicate the same or equivalent part in all these figures.

It may be desirable to fill the fuse with an indifferent protective gas and in such case the capillary and the electrodes will be enclosed in a glass bulb or the like.

While specific embodiments of my invention have been shown and described in detail to illustrate the application of the principles of my invention, it will be well understood that the same may be otherwise embodied without departing from such principles and with out avoiding the scope of the appended claims.

What I claim as my invention is:

1. An electric fuse comprising in combination a first capillary member made of an electrically insulating material adapted to receive and to hold a filament of an electrically conductive liquid medium; an open wider capillary member at each end of said first capillary member forming lateral extensions thereof and adapted to hold by capillary action a supply of said liquid medium; a heat insulating disc between the first capillary member and each of the adjoining wider capillary member; a closed casing enclosing said capillary member; two electrodes each extending through one of said wider capillary member into said first capillary member; and electric leads to said electrodes.

2. An electric fuse comprising in combination a closed casing; within said casing a member made of an electrically insulating material and containing a capillary adapted to receive and to hold a filament of an electrically conductive liquid medium; said capillary being widened at each end to hold still by capillary action a supply of said liquid medium, two electrodes reaching into the middle portion of said capillary from opposing ends thereof said electrodes being made from twisted fiat wire; and electric leads to said electrodes.

3. An electric fuse comprising in combination a member made of an electrically insulating material and ineluding a capillary adapted to receive and to hold a filament of an electrically conductive liquid medium; said capillary including a capillary central section arranged between adjoining wider capillary outer sections; at least the central portion of said member containing the said central section of the capillary being made of transparent material; a closed casing surrounding said member; at

least a portion of said casing being transparent to permit observation of said filament within said capillary central section; two electrodes mounted in said casing, each electrode extending through one of said outer capillary sections into said central capillary section; a phosphorescent layer partially enclosing said central portion of said member at least opposite the ends of said electrodes, and electric leads to said electrodes.

4. An electric fuse comprising in combination a closed casing; within said casing a pair of parallel axial bodies made of an electrically insulating material; opposing plane surfaces upon said bodies extending in axial direction thereof; said plane surfaces spaced to form a slit capillary; two electrodes reaching into the middle portion of said capillary from opposing ends thereof; and electric leads to said electrodes.

5. An electric fuse comprising in combination a closed casing; within said casing a pair of bodies made of an electrically insulating material; opposing plane surfaces upon said bodies extending in axial direction thereof; said plane surfaces spaced to form a slit capillary; the outer portions of said plane surfaces being more spaced than the middle portions thereof to form widened capillaries; two electrodes reaching into the middle portion of said capillary from opposing ends thereof; and electric leads to said electrodes.

6. An electric fuse comprising in combination an open casing; a cover for said casing; a pair of bodies made of a transparent and electrically insulating material; one of said bodies seated in said casing; the other body seated in said cover and having a lenslike middle portion; opposing plane surfaces upon said bodies; said plane surfaces spaced to form a slit capillary; two electrodes reaching into the middle portion of said capillary from opposing ends thereof; a longitudinal window in said cover exposing the said lenslike middle portion of said other body and the opposing ends of said electrodes; and electric leads to said electrodes.

7. An electric fuse comprising in combination a closed casing; in said casing a member made of an electrically insulating material and including a capillary adapted to receive and to hold by capillary action a filament of an electrically conductive liquid medium; said capillary having at either end continuing widened portions open at their outer ends; two electrodes reaching into the middle portion of said capillary from opposing ends thereof; and electric leads to said electrodes.

8. An electric fuse according to claim 7 wherein the widened end portions of the capillary are arranged in separate members made of an electrically insulating material.

References Cited in the file of this patent UNITED STATES PATENTS 1,392,873 Illingworth Oct. 4, 1921 1,699,769 Ulrey et al Jan. 22, 1929 2,063,813 Kellendorfer Dec. 8, 1936 2,306,728 Heddaeus Dec. 29, 1942 2,485,778 Ryles Oct. 25, 1949 

